The present invention relates to a speed change control system for an automatic transmission for motor vehicles.
The automatic transmission having a planetary gear train has a brake band which is operated by a servo-mechanism for altering the transmission ratio. If the oil pressure for the servomechanism increases rapidly, the brake band is suddenly tightened. As a result, a large shock in the speed change operation occurs. Heretofore, in order to reduce the speed change shock, an orifice is provided in an inlet port of the oil chamber for the servo-piston, so that the pressure of the oil may slowly increase. However, such a device cannot sufficiently eliminate the speed change shock.